Recently, researches are conducted on the Multiple-Input Multiple-Output (MIMO) system using spatial resource for transmitting high quality data at a high data rate in a wireless communication environment.
The MIMO system can be classified into one of Single-User MIMO (SU-MIMO) for allocating one time-frequency resource to a single user and a Multi-User MIMO (MU-MIMO) for allocating one time-frequency resource to multiple users through spatial multiplexing.
FIG. 1 illustrates a diagram of a MIMO system between a base station and a plurality of users.
Referring to FIG. 1, the base station 110 and one or more terminals 130 are capable of communicating data through the radio channel 120. The channel information feedback 140 may be implemented through the radio channel 120 from the terminals 130 to the base station 110.
The base station 110 may include a scheduler 112 for scheduling data addressed to the terminal 130, a precoder for precoding the data streams scheduled by the scheduler 112, and a transceiver 116 for transmitting the precoded signals to the terminal 130 and receiving the signals transmitted by the terminals 130.
In a reference technology, the base station 110 may operate in a downlink communication mode of 3rd Generation Partnership Project Long Term Evolution (3GPP LTE). The base station 110 receives at least one of Precoding Matrix Index (PMI), Channel Quality Indicator (CQI), and Rank Indicator (RI) from the terminals 130; and performs precoding on the data based on the received information by means of the precoder 114 and transmits the precoded data. The data are precoded using a unitary matrix and then transmitted.
In the 3GPP LTE downlink communication mode, each terminal 130 feeds back at least one of PMI, CQI, and RI determined based on the state of the channel 120 and received quality.
In the downlink system operating in SU-MIMO mode, the interference affecting to the terminal is mainly determined depending on the signals from the neighbor base stations. In the downlink system operating in MU-MIMO mode, however, the signals transmitted on the different layers of the same time-frequency resource also may act as interference in addition to the signals transmitted by the neighbor base station, resulting in influence to the system performance.
The current 3GPP LTE-based terminal is capable of estimating the interference signals of neighbor base stations and thermal noise but not the inter-layer interference signals in MU-MIMO mode. For this reason, in the MIMO downlink system, the terminal feeds back PMI, CQI, and RI generated without reflecting the influence of inter-layer interference signals to the base station, resulting in performance degradation. There is therefore a need of a data communication method and apparatus capable of taking in consideration of inter-user interference in the MU-MIMO system.